PBI Hollow fibers for pervaporation dehydration of acetone

Abstract

Acetone dehydration via pervaporation is challenging because acetone and water have close molecular sizes and acetone has a much higher vapor pressure than water. Acetone is also a powerful solvent which dissolves or swells most polymers. We have developed novel polybenzimidazole/BTDA-TDI/MDI (PBI/P84) dual-layer hollow fibers for pervaporation dehydration of acetone for industrial and biofuel separations. Both thermal and chemical cross-linking modifications were applied to the membranes in order to investigate their effectiveness to overcome acetone-induced swelling. Thermal treatment can effectively enhance separation performance, but performance stability can only be achieved through the cross-linking modification of PBI. Cross-linking by p-xylene dichloride followed by a thermal treatment above 250 °C show significant effectiveness to improve and stabilize pervaporation performance. The fractional free volume of the PBI selective layer reduces from 3.27% to 1.98% and 1.33%, respectively, after thermal treatment and a combination of chemical/thermal cross-linking modifications characterized by positron annihilation spectroscopy.